1. Field of the Invention
The present invention generally relates to a polymerizable liquid crystal composition and an optical anisotropical body obtained therefrom, and further relates to an optical compensation element and an optical element that uses the optical anisotropical body.
2. Description of Related Art
Polymerizable liquid crystal compounds having a liquid crystal phase can be used to obtain a polymer having optical compensation functions through polymerization. That is, the alignment of the liquid crystal compound is fixed through polymerization. In order to take advantages of the features of such polymers, a variety of polymerizable liquid crystal compounds have been developed.
However, a single polymerizable liquid crystal compound cannot meet sufficient functionality. In patent documents 1-4, compositions were prepared from a variety of polymerizable liquid crystal compounds, wherein the composition was polymerized.
For polymers having homeotropic alignment, the direction of the optical axis is in the nz direction, and since the refractive index in the optical axis direction is larger than the refractive index in an orthogonal direction, the refractive index ellipsoid is classified as positive C-plate. In non-patent document 1 and non-patent documents 2, 5 and 6, for optical compensation of the liquid crystal mode where the liquid crystals are horizontally aligned during black display or so-called IPS (In-Plane Switching) mode, and the like, for example, in order to improve the viewing angle characteristics of the polarizers, the positive C-plate is combined with films having other optical functions.
In the above applications, there are situations where the polymerizable liquid crystal material is laminated onto a supporting substrate such as glass substrate or plastic substrate. Examples of the materials used as the plastic substrate are such as polymers of TAC (triacetyl cellulose), polycarbonate, PET, acrylic resins and cycloolefin resins.
For making the polymerizable liquid crystal compound to have homeotropic alignment, patent document 7 discloses that when the supporting substrate is a glass substrate, the structure of the polymerizable liquid crystal compound is selected for expressing smectic phase. For making the polymerizable liquid crystal compound to have homeotropic alignment, patent document 8 discloses that lecithin is applied on the glass substrate as a vertical alignment film. In patent documents 1 and 9, an alignment film is formed on the plastic supporting substrate.
In patent documents 10, 11 and 12, even without forming an alignment film on the supporting substrate, methods for preparing a uniform polymerizable liquid crystal compound having homeotropic alignment are disclosed. For instance, patent document 12 discloses a polymerizable liquid crystal compound having a monofunctional polymerizable functional group. However, for the optical anisotropical body obtained by polymerizing the compositions described in patent documents 10, 11 and 12, the anisotropy is lowered due to heat and deterioration is significant due to the contact with solvents.